1. Field of the Invention
The present invention relates to a stepping motor control circuit, a movement having the stepping motor control circuit, and an analogue electronic timepiece using the movement.
2. Description of the Related Art
In the related art, a stepping motor including a stator having a rotor housing through hole and a plurality of positioning portions for determining a stable still position of a rotor, the rotor disposed in the rotor housing through hole, and a driving coil wound around the stator is used in analogue electronic timepieces or the like. The stepping motor described above is configured to perform detection of rotation in order to achieve further reliable rotation. (See Japanese Patent No. 3757421 and International Publication No. 2005/119377, for example).
In an invention disclosed in Japanese Patent No. 3757421, a stepping motor driving coil and a rotation detecting coil are wound one on top of another on a stator in order to detect a rotation of a stepping motor, and the rotational driving of the stepping motor is performed by the driving coil, and detection of rotation is performed by the rotation detecting coil.
Since the driving coil and the rotation detecting coil are used, the detection of rotation may be performed by the rotation detecting coil in parallel with the driving even within a period when the stepping motor is driven by a drive pulse, and hence detection of rotation with high degree of accuracy is possible.
However, since the rotation detecting coil specific for the detection of rotation, which is different from the driving coil, is used for the detection of rotation, there is a problem that the stepping motor is complicated in configuration and increased in size.
In contrast, International Publication No. 2005/119377 discloses an invention in which a stepping motor is rotationally driven by using main drive pulses P1 in a plurality of energy ranks. A rotor is rotated by a main drive pulse P11, then if an induced signal VRs generated by free vibrations of the rotor is reduced to a level lower than a predetermined reference threshold voltage Vcomp, the stepping motor is driven by a corrected drive pulse P2 having energy larger than the respective main drive pulses P1, and the main drive pulse P1 used for the next drive is ranked up to a main drive pulse P12 having energy larger than the main drive pulse P11.
When the rotor is rotated by the main drive pulse P12, the induced signal VRs exceeding the reference threshold voltage Vcomp is detected, and when the time-of-day when the induced signal VRs is detected is earlier than a reference time-of-day, it is determined that the energy is too large, and the main drive pulse P12 is ranked down to the main drive pulse P11. Accordingly, the rotor is rotated at the main drive pulse P1 in accordance with a load during the drive, whereby a current consumption is reduced.
In an invention disclosed in International Publication No. 2005/119377, since rotary driving and detection of rotation of the stepping motor are performed by using a driving coil, complication of configuration as the invention described in Japanese Patent No. 3757421 is avoided.
However, according to the invention in International Publication No. 2005/119377, the rotation is detected during a detection period DT provided after the completion of driving by the main drive pulse P1.
Therefore, in a case of the main drive pulse P1 having large energy, the induced signal VRs exceeding the reference threshold voltage Vcomp is generated within a driving period P of the main drive pulse P1, and only induced signals VRs which do not exceed the reference threshold voltage Vcomp are generated during the detection period DT.
Therefore, there is a problem of erroneous determination such that the rotor is not rotated even it is rotated may occur. When it is determined erroneously that the rotor is not rotated, the rotor is rotationally driven by using a corrected drive pulse P2 having energy larger than the main drive pulse P1. Therefore, there are fears of large power consumption and an extremely shortened battery life.
JP-A-2010-145106 discloses an invention in which a pulse down counter circuit configured to output a pulse down control signal for performing pulse-down control of a main drive pulse P1 on a first cycle or a second cycle longer than the first cycle is provided, a rotation detection period is divided into a first detection time interval immediately after the driving by a main drive pulse, a second detection time interval coming after the first detection time interval, and a third detection time interval coming after the second detection time interval, and when a rotation detection unit detects an induced signal VRs exceeding a reference threshold voltage Vcomp, a pulse down cycle of the pulse down counter circuit is changed to the second cycle to allow earlier pulse down.
However, since two counters, one having a short cycle and the other having a long cycle, are provided in the invention disclosed in JP-A-2010-145106, a large space is occupied if a stepping motor control circuit is configured as an integrated circuit (IC), and hence there arises a problem of difficulty in reduction in size.
JP-A-2010-220461 discloses an invention in which a detection time interval in which a condition of rotation is detected is divided into a plurality of time intervals, and when performing pulse down, a detection value from a time interval T2 is used for control, and considering variations caused by mass production and the safety degree of operation, pulse control is performed aiming that detection of an induced signal VRs exceeding a reference threshold voltage Vcomp is achieved in a latter half of a time interval T2 (time interval T2B) indicating that drive allowance is reduced.
In the configuration in JP-A-2010-220461, the pulse down is performed when a state in which the induced signal VRs exceeding a predetermined value is detected in the time interval T2B (a state in which the drive allowance is small) occurs continuously by a predetermined first number of times and, when a condition of rotation having a large drive allowance occurs even through the condition of rotation in which the drive allowance is small does not occur continuously by the predetermined first number of times, the pulse down is also performed before the occurrence of the state described above continuously by the first number of times.
Accordingly, a reduction of power consumption is enabled with stabilized operation by performing the pulse down in a shorter time when the drive allowance is large, and performing the pulse down in a longer time when the operation is stabilized even though the drive allowance is small.
However, since the pulse down is performed only when the state of having a sufficient energy allowance results continuously by the predetermined number of times, there is a problem of waste of energy until the pulse down is performed.
The invention disclosed in JP-A-2010-220461 is also configured in such a manner that when the induced signal VRs exceeding a reference threshold voltage Vcomp is generated in a time interval T1, the rank is maintained even when the induced signal VRs exceeding the reference threshold voltage Vcomp is generated in any one of a front half (time interval T2A) and the latter half (time interval T2B) of the time interval T2. When the induced signal VRs exceeding the reference threshold voltage Vcomp is detected in the time interval T2A, the pulse down is not performed even though sufficient drive allowance exists and hence the state allows pulse down, so that there is a problem of wasted power consumption.